This invention relates to a polymer pattern forming method.
In the communications field, communications networks using light have to be constructed in order to achieve high capacity transmission. The development of interconnection systems and optical wave guide components, and reducing the cost of parts, are therefore matters of major importance.
In the past, glass or inorganic crystalline materials were used in parts such as for example optical wave guide components, however these materials are costly and forming them into a desired shape is difficult.
Therefore, in recent years, polymer materials such as PMMA (polymethylmethacrylate), which are less expensive and easier to work than glass or inorganic crystalline materials, have come to be used instead. If these materials are used, it is possible to form a film-type optical wave guide with greater surface area and excellent flexibility. Also, if functional compounds or functional groups are introduced into these polymer molecules, functional optical wave guides can be engineered.
To manufacture components such as optical wave guides, techniques are required to form the polymer material to a desired pattern. In the prior art, polymer patterns on substrates were mainly formed by reactive ion etching (RIE) using an oxygen plasma.
However, the equipment used for RIE is expensive, and a high level of skill is required to operate it. Also, prior to etching, it is necessary to provide an etching mask corresponding to the pattern on the polymer to be etched by lithography.
To form a polymer pattern using RIE, steps shown schematically in FIG. 3A to FIG. 3E, for example, must be followed. FIG. 3A to FIG. 3E are sectional views showing, in sequence, the main steps involved in forming a polymer pattern by RIE.
First, a polymer film 103 is formed on a substrate 101, and a photoresist film 105 is formed on this polymer film 103 (FIG. 3A). Next, to form this photoresist film 105 so that it can be used as an etching mask corresponding to a desired pattern, photolithography is performed using a photomask 107 corresponding to the pattern (FIG. 3B). A pattern latent image 109 is thereby formed in the photoresist film 105. Part of this pattern latent image is removed by etching (alternatively only part of the pattern latent image may be allowed to remain) so as to form a resist pattern 105x (FIG. 3C). Subsequently, RIE is performed using this resist pattern 105x as an etching mask 105x, to remove the exposed part of the polymer film 103 (FIG. 3D). Finally, the etching mask 105x is removed (FIG. 3E), leaving a polymer film on the substrate 101 forming a polymer pattern 103x. Hence, a large number of steps were involved in the process, and considerable time was required to form the pattern.
A low-cost, simple polymer pattern forming method was therefore desired.
The inventors of the present invention, by bringing a monomer having radical polymerizing properties into contact with a part generating radicals, were able to addition-polymerize the monomer onto the radical generating part, and thereby arrived at the present invention.
The polymer pattern forming method of this invention comprises a step of generating radicals in a pattern forming region of a matrix layer uniformly containing a radical generating agent, thereby forming a pattern latent image due to the radicals in the pattern forming region, and a step of bringing a radical polymerizing monomer into contact with the matrix layer in which the pattern latent image has been or is being formed, to have these radicals which have been or are being generated induce a chain addition polymerization of the monomer so as to form a polymer pattern in the pattern forming region.
Until now, in the RIE method, the polymer pattern could be formed only by going through a large number of steps using costly equipment. According to this invention however, a pattern latent image due to radicals is formed by exposing an underlying layer, and a radical polymerizing monomer is then brought in contact with the pattern latent image. As the steps to provide an etching mask and then remove the mask are unnecessary, a desired polymer pattern can be formed on a substrate in far fewer steps than in the prior art, consequently, there is no need for any expensive equipment and the polymer pattern can be formed with ease.
Preferably, the radicals are generated by radiation. This radiation may be in the form of electromagnetic waves of any wavelength including light and electron beams, but must have sufficient energy to convert a radical generating agent to radicals. Here, it is convenient to irradiate the pattern forming region by light. This light may for example be ultraviolet radiation. The radical generating agent used in this invention can be converted to radicals using light of wavelength 280 nm-500 nm. Preferably, the light should not have a wavelength of less than 280 nm or more than 450 nm so as not to destroy a matrix layer. Areas of the matrix layer containing the radical generating agent other than the region in which the pattern is to be formed (pattern forming region) are covered by a photomask, the radical generating agent in the pattern forming region is converted to radicals by exposure to light, and a pattern latent image is formed by the radicals. A radical polymerizing monomer is then brought in contact with the matrix layer in which the pattern latent image has been formed to induce addition polymerization of the monomer, and a polymer pattern matching the pattern latent image is thus easily formed.
The radical polymerizing monomer may be brought into contact with the matrix layer at the same time as the generation of the radicals. In this case, the generation of the radicals by for example radiation, and the addition polymerization of the monomer by the contact of the radical polymerizing monomer with the matrix layer take place concurrently.
It is also preferable that the matrix layer is formed by mixing a material having radical polymerizing properties with a radical polymerizing agent, the latter being present in greater amount than is required to polymerize the material, and to polymerize the material using part of the radical generating agent.
According to this invention, to form the polymer pattern on the matrix layer, the matrix layer must contain a radical polymerizing agent. For this purpose, a material having radical polymerizing properties and an excess amount of a radical polymerizing agent are used for the matrix layer. First, after mixing the materials together, the matrix layer is exposed to light to generate radicals, and the material having radical polymerizing properties is polymerized. A hard matrix layer is thereby obtained. As the amount of radical generating agent used is greater than the amount required to harden the material having radical polymerizing properties, some radical polymerizing agent which has not been converted into radicals remains in the hardened matrix layer. The matrix layer is therefore made to contain radical generating agent. When a mask corresponding to the pattern is provided on the matrix layer and the matrix layer is exposed to light, the radical generating agent in the matrix layer which is exposed through the mask is converted to radicals, and due to these radicals, a pattern latent image is easily formed.